Injectors are in widespread use, in particular for combustion engines where they may be arranged in order to dose a fluid into an intake manifold of the combustion engine or directly into a combustion chamber of a cylinder of the combustion engine.
In general, an injector has tough performance requirements to enable injection of accurate quantities of fluid and to fulfill pollution restrictions during operation of the injector and the corresponding combustion engine. Two main requirements are the ability to open at high pressures, for example higher than 200 bar in case of gasoline engines, and to enable fast closing times, for example less than 500 microseconds, in order to have a low flow and low actuation time.
Such requirements, for example also concern hydraulic valves like solenoid actuated valves. Regarding a solenoid injector, the mentioned requirements can be fulfilled using a free lift concept in which an armature, for example, travels a small portion of a total lift without carrying a valve needle. In a next step, the armature impacts the valve needle and opens the injector through an impulse that overcomes the necessary force to open the valve needle and the injector at high pressures and further allows for a fast opening transient.
Due to the impact of the armature on the valve needle, a velocity of the valve needle is high during opening and travel phases. On the one hand, the opening of the injector is desirable to be fast but on the other hand it is requested that a remaining portion of the impact on the valve needle leads to a limited velocity in order to make an operation of the valve needle and the injector controllable during ballistic operations, for example. In this context, a controllability of the injector refers to a variation of flow of a fluid versus changes of time of activation.